In wireless communications networks, the MMSE algorithm may be used to reduce the effect of interference between MIMO antenna streams. When using OFDM/OFDMA (Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiple Access) in WiMAX transmissions, each frame 10 is divided into a plurality of sub-carriers 12, defined by frequency and symbols over time 14, as shown schematically in FIG. 1. In order to estimate the channel for purposes of data processing, pilot signals 16 are transmitted together with the data. Since both receiver and transmitter know the pilot signal, the channel can be estimated and the estimation can be used to reduce interference for the received data.
One example of a group of sub-carriers in a frame is a WiMAX tile 18, a unit formed of three symbols by four subcarriers, typically with one pilot in each corner of the tile.
In WiMAX tiles, channel variations are typically phase shifts per column combined with phase shifts per row—that is, a combination of time related and frequency related phase-shifts. In conventional methods, the MMSE calculation is performed in the receiver several times, once for each pilot of each tile, involving a substantial computational cost. As bandwidth increases, the number of tiles increases and the quantity of computations increases still further.
Accordingly, there is a long felt need for a method of reducing the complexity of MMSE computations per group of sub-carriers, that provides satisfactory results but requires substantially fewer computations than the conventional channel estimation method.